1. Field of the Invention
This invention relates to a vibration type actuator such as a vibration type motor having an output shaft.
2. Related Background Art
A bar-like vibration wave motor as a vibration actuator has as basic construction a vibration member having a piezoelectric element as an electro-mechanical energy conversion element sandwiched between elastic members, and a rotatable member pressure-contacting the driving surface of the vibration member, for example, the end surface of this vibration member. This type having an output shaft is disclosed in Japanese Laid-Open Patent Application No. 1-252178. The bar-like vibration wave motor of this type having an output shaft, as shown in FIG. 5 of the accompanying drawings, has a bar-like vibration member 180 disposed in an outer case 190, and has one end portion of the vibration member 180 supported on a bottom lid 135. Two bearings 140 are provided on one end portion of the outer case 190, and an output shaft 113' fixed to the rotatable member 113 is supported by the bearings 140. Balls 110, 112 and 115 supported by retainers 109, 111 and 114, respectively, are successively stacked on the other end side of the vibration member 180, and the rotatable member 113 is brought into pressure contact with the balls 115 by a spring 138, one end of which is supported by a thrust bearing 139 mounted in the case 190. When a driving signal is applied to the piezoelectric element of the vibration member 180, the vibration member rotates the above-mentioned balls and the rotatable member 113 is rotated and the output shaft 113' is also rotated.
In the above-described example of the prior art, however, the output shaft is disposed only on one side of the vibration member and, therefore, the distance between the two bearings supporting the output shaft is short. On the other hand, a rotational force transmitting member such as a gear or a pulley is usually mounted on the output shaft. When an external load is applied to the rotational force transmitting member, a side force is applied to the output shaft, and the output shaft becomes inclined. As a result, the frictional sliding surface is subjected to an offset load and, thus, a uniform frictional driving force is not created, and a reduction in service life is caused by a reduction in motor efficiency, the creation of noise and the offset wear of the frictional material.